The prototype of the Boeing 707 was the first jet transport to be completed and flown in the United States. Its first run was on July 15, 1954, and was known as the Model 36780. Under the designation of KC-135, it was used by the U.S. Air Force for air-to-air refueling. In 1955, the Air Force permitted Boeing to produce commercial versions of the transport. These became known as the 707 and 720. The 707-120 was the first production version and was primarily designed for domestic use, though capable of over-ocean operations. Power was provided by four 13,000-lb. s.t. turbojets. The 707-220 followed with its 15,800-lb. s.t. Pratt & Whitneys. The 707-320 was the first intercontinental version and featured increased fuselage length and was powered by either 15,800- or 16,800-lb. s.t. turbofans. Accommodations provided for 195 to 219 economy class passengers. The usual arrangement was 14 first-class seats with 133 coach seats.